Metallurgical processing for surface science research typically involves the examination of a sample in a vacuum chamber of an examination instrument, generally in an ultra high vacuum (UHV) condition, which can be defined as a pressure which is below 10−7 Torr, and may be down to 10−9 Torr, or lower. Typically, samples are prepared for such research in separate instruments, before an appropriate sample is introduced to a UHV examination chamber.
Such preparation typically involves one or both of two important stages, comprising (1) drying and (2) fracturing, each of which presents problems.
In the drying stage, metallurgical samples, which are generally wet, can be dried for analysis by various known methods, which include drying in an inert gas environment in a suitable container. Another known method is drying in a forechamber which is available as an attachment to known examination instruments. This method, developed at the Ian Wark Institute in Adelaide, Australia, is described in the text Minerals Engineering, 1991, Smart, R. St. C., vol. 4, pp. 891-909.
There are problems arising from the use of either of these two principal known methods of drying samples for analysis.
In relation to the first method, where a sample is dried in an inert atmosphere not directly connected to the examination instrument, there are risks of adverse effects during transport to the instrument, including from air exposure.
However, in relation to the second method, i.e. where a sample is not dried in a remote location, but in a forechamber to the instrument, or in the examination chamber itself, although the air exposure risk is reduced or removed, there are two important disadvantages. Firstly, there is a risk of adverse effect on the UHV conditions of the examination chamber when the sample is moved into that chamber; and secondly, there is the problem that arises from the length of time required for preparation of such samples in the forechamber. Although a typical forechamber is designed to be pumped down to the desired vacuum condition in a relatively short period, of approximately twenty minutes, the process is of necessity substantially longer, often many hours, for proper preparation of metallurgical samples. While such samples are in the forechamber, or the examination chamber itself, the examination chamber cannot be accessed for other work, and valuable instrument time is thus lost.
In the second stage of sample preparation for surface science research, i.e. the fracturing of the sample to obtain a suitable surface for analysis, the methods currently in use also raise problems.
For example, U.S. Pat. No. 3,720,829 to Palmberg teaches the fracturing of samples within an examination chamber to be operated in a high vacuum condition. As the vacuum of the chamber is broken each time that a sample is placed in the chamber, the vacuum level is required to be repeatedly reestablished. Even to attain only a high vacuum condition, rather than the UHV condition of the present invention, can take several days, during which the examination chamber could not be used for other purposes.
Further problems arise in relation to the fracturing method itself. Typically, current methods of fracturing involve a high energy impact, for example impact by the use of a hammer and chisel in a UHV chamber, after freezing of the sample to an extremely low temperature, generally below 75 K. However, if this method is used for a brittle material, the entire sample can be destroyed. If instead fracturing is performed in an inert gas in a location which is remote from the examination instrument, there is a serious risk of contamination during transfer to that instrument, the risk being increased by the more reactive nature of the surfaces which have been exposed by fracture. Further limiting factors at this stage include the shape and size of samples.
Typically also, a single chisel is used, which is generally effective in many situations. However, it has been found that for metallurgical samples, greater effectiveness and precision can be achieved, without high impact and without any manifest disadvantages, by the use of a pair of chisels, preferably in opposed directions in relation to each other.
It has been found that a UHV conditioning chamber can be provided which can be attached to, and directly connected with, a UHV examination chamber; and in which a sample can be prepared by drying and fracturing for subsequent transfer into the examination chamber, without leaving the desired UHV condition, thereby avoiding the problems associated with the extended drying time which may be required, and with the risks presented by transfer from a remote drying location to the examination chamber.
It has also been found that the use of vacuum pumps of more than one type can improve the attainment of the desired UHV condition. It has further been found that the use of appropriate retaining means within the chamber can enable the use of dual chisels for fracturing, with consequent improved quality and reduced risk of damage to the sample during fracturing. Further, it has been found that the retaining means for the sample within the conditioning chamber can be combined with suitable transporting means to move the prepared sample into the examination chamber of an instrument through a connecting means.
The invention seeks to provide a conditioning chamber, and a method of conditioning samples in a conditioning chamber, which is suitable for samples of irregular shapes, a wide range of sizes, and different conditions, including slurry conditions. The condition chamber includes an improved UHV environment for drying metallurgical samples for analysis in UHV instruments, and in which the surface preparation by fracturing can also be performed, thus minimizing the risks of contamination from exposure to air or other changed conditions during transfer.
The invention further seeks to provide improved sample retaining and fracturing means which substantially reduce or eliminate the risk of destruction of or damage to samples during the fracturing process.